The present invention is directed to temperature sensors and, more particularly, to snap-action thermal switches and electrical temperature sensors.
Snap-action thermal switches are utilized in a number of satellite applications, such as temperature control of batteries and hydrazine lines, and for overheat detection of mechanical devices such as motors and bearings. Current snap-action thermal switch designs typically provide open and closed functions only, whereby temperature data is available only at the instant the thermal switch operates. Current practice thus necessitates hard wiring of additional temperature sensors to sense a range of temperatures. These additional temperature sensors are typically installed in systems as subsystems that stand apart from the snap-action thermal switch systems that provide overheat protection, and thus increase overall system complexity and weight. Such additional temperature sensor subsystems are typically less reliable than a snap-action thermal switch. Overall system reliability is generally degraded when such additional temperature sensor subsystems are relied upon.
The present invention overcomes the limitations of the prior art by providing a multiple output thermal detection and protection device that is capable of providing an output signal representative of the temperature sensed by the device, and further providing a positive output signal representative of the sensed temperature reaching a predetermined set point temperature.
The invention is embodied, for example, in a first two-terminal device having first and second terminals extending through and to both sides of a substantially planar header, the terminals being electrically isolated from the header. The first two-terminal device also includes a first stationary contact fixed adjacent to one end of the first terminal; a second contact fixed adjacent to one end of the second terminal and being movable between a first position spaced away from the first stationary contact in an open circuit structure and a second position in contact with the first stationary contact in a closed circuit structure; an upright tubular spacer fixed to and projecting from the header and surrounding the first and second contacts and the portions of the first and second terminals adjacent to the contacts; a housing fixed to the header and enclosing all of the spacer, the first and second contacts, and the portions of the first and second terminals adjacent to the contacts, the housing also extending beyond the spacer and cooperating with the spacer to form an annular space therebetween spaced away from the contacts; a bimetallic disc actuator captured within the annular space and being responsive to a sensed temperature of a predetermined set point to change state between a concave and a convex relationship to the electrical contacts, such that the disc actuator spaces the movable contact away from the stationary contact when in the concave relationship and the disc actuator permits the movable contact to contact the stationary contact when in the convex relationship; and an electrical temperature sensor sharing the first and second terminals in common with the respective first and second contacts and being structured to provide an output on one of the first and second terminals that is representative of the sensed temperature.
According to one aspect of the first embodiment of the invention, the disc actuator is structured to be in the concave relationship to the electrical contacts when the sensed temperature is below the predetermined sensed temperature, such that the circuit formed by the first and second contacts is open with the movable contact spaced away from he fixed contact, and the output of the electrical temperature sensor is available on the first nd second terminals.
According to another aspect of the first embodiment of the invention, the electrical temperature sensor is one of a resistance temperature detector (RTD), a platinum resistance thermal device (PRTD), a thermistor, a thermocouple, and a monolithic silicon temperature transducer.
The invention is also embodied, for example, in a three-terminal multiple output thermal detection and protection device having the output of the electrical temperature sensor is available whether the circuit formed by the first and second contacts is open or closed. Accordingly, the invention embodied as a three-terminal multiple output thermal detection and protection device includes: first, second and third terminals extending through and on either side of a substantially planar header, the three terminals being electrically isolated from the header and from one another; a first stationary contact fixed adjacent to one end of the first terminal; a second contact fixed adjacent to one end of the second terminal and being movable between a first position spaced away from the first stationary contact in an open circuit structure and a second position in contact with the first stationary contact in a closed circuit structure; an upright tubular spacer affixed to and projecting from the one side of the header and surrounding the first and second contacts, the portions of the first and second terminals adjacent to the contacts, and the third terminal; a housing enclosing the spacer, the first and second contacts, the portions of the first and second terminals adjacent to the contacts, and the third terminal, the housing extending beyond the spacer and cooperating with the spacer to form a space therebetween spaced away from the contacts; a bimetallic disc actuator captured within the space between the spacer and the housing and being responsive to a sensed temperature at or near a predetermined set point for changing state between a first pressing upon and a second spaced away relationship to the movable electrical contact, such that the disc actuator spaces the movable contact away from the stationary contact when in the first pressing upon relationship and the disc actuator permits the movable to move into contact with the stationary contact when in the second spaced away relationship; and an electrical temperature sensor sharing one of the first and second terminals in common with the respective first and second contacts and being coupled to the third terminal for providing an output signal representative of the sensed temperature.
According to one aspect of the three-terminal embodiment of the present invention, the disc actuator is structured to be in either of the first pressing upon relationship and the second spaced away relationship to the electrical contacts when the sensed temperature is below the predetermined sensed temperature.
According to still other aspects of the invention, the snap-action thermal switch is embodied as four-terminal and five-terminal switches.
According to another aspect of the three-terminal embodiment of the present invention, the electrical temperature sensor is one of a resistance temperature detector (RTD), a platinum resistance thermal device (PRTD), a thermistor, a thermocouple, and a monolithic silicon temperature transducer.
The invention also provides methods of accomplishing the same.